In a planimeter, signals according to rotation of a measuring lever, and a wheel during tracing of a figure to be measured are counted. It is necessary to clear (i.e., zero) the counters at the original or starting position, (i.e., right angle position of the measuring lever against the axis of the wheel). Heretofor, as shown in FIG. 4a, displacement of wheel 1 and measuring lever 3 are detected by encoders 6, 7 and their signals, a, b tabulated by counters 25, 26. Sensor G generates a specific pulse when measuring lever 3 passes the original point, and as shown in FIG. 4b, at step G1, an operator should move measuring lever 3 past the original point for clearing counters 25, 26. However step G1 operation is an inconvenience.
In use, an operator should trace a figure to be measured by tracing each part through a lens, but a figure is often out of the field of sight.
Moreover, variations because of the length of the measuring lever introduces errors and adjusting for the length is a troublesome matter.